1. Field of the Invention
This invention relates to a magnetic recording system, and especially to a magnetoresistive head utilizing magnetoresistance effects, the head being suitable for use in a magnetic disc system, and also to a fabrication process thereof.
2. Description of the Related Art
As a magnetic head capable of reading data at high sensitivity from a magnetic surface of a magnetic recording medium, a magnetoresistive head making use of magnetoresistance effects is known. Utilizing magnetoresistance effects whereby the electrical resistance of a magnetoresistive film varies depending on the direction of magnetization of a magnetic recording medium, this magnetoresistive head converts magnetic signals on the recording medium into electric signals.
Such a magnetoresistive head is, however, accompanied by the problem that it produces noise called "Barkhausen noise" as a result of irregular shifts of domain wails, which are contained in a magnetoresistive film, by magnetic fields of signals on a recording medium.
To reduce the noise, U.S. Pat. Nos. 4,103,315, 4,809,109 and 5,014,147 disclose the provision of an antiferromagnetic layer over the whole of one side of a magnetoresistive film to produce a longitudinal bias magnetic field, which is uniform in the longitudinal direction thereof, so that domain walls in the magnetoresistive film can be eliminated utilizing magnetic exchange coupling between the antiferromagnet and the ferromagnet. The term "magnetic exchange coupling" as used herein means coupling that brings the direction of spins in an antiferromagnetic film into conformity with the direction of spins in a ferromagnetic film in the vicinity of an interface between the antiferromagnetic film and the ferromagnetic film. A layer provided to apply a longitudinal bias magnetic field in order to suppress the occurrence of magnetic walls in a magnetoresistive film will hereinafter be called a "domain wall suppressing layer".
The above-described construction wherein an antiferromagnetic film is laminated as a domain wall suppressing layer over the whole of one side of a magnetoresistive film, however, has large magnetic exchange coupling between the antiferromagnet and the ferromagnet, thereby making it difficult to rotate magnetic moments in the magnetoresistive film. As a consequence, the magnetic moments in the magnetoresistive film are difficult to rotate by magnetic fields of signals on the medium, resulting in a reduction in the sensitivity of the magnetoresistive film to the magnetic fields of signals on the medium.
With a view toward overcoming the above problem, U.S. Pat. Nos. 4,663,685 and 5,005,096 have been proposed. These patents are each concerned with a magnetoresistive transducer head. According to the inventions of these patents, domain wall suppressing layers are formed only at opposite end portions of a magnetoresistive film, respectively, to prevent Barkhausen noise without lowering the sensitivity of the magnetoresistive film to the magnetic fields of signals on a recording medium. Contemplated materials for the domain wall suppressing film include Fe-Mn alloys as antiferromagnetic materials and Co-Pt alloys as permanent magnet materials. The state of a single domain, which is maintained by the domain wall suppressing layers at the opposite end portions, also converts into a single domain a central magnetism sensing portion where no domain wall suppressing layer is disposed. Prerequisites for the conversion of the central portion into a single domain by the domain wall suppressing layer provided at the opposite end portions include a large exchange coupling field, a wide area of contact between the domain wall suppressing layers and the magnetoresistive film, and a small distance between the domain wall suppressing layers arranged at the opposite end portions of the magnetoresistive film.
The construction wherein antiferromagnetic films acting as domain wall suppressing layers are formed only at opposite end portions of a magnetoresistive film as described above can convert the whole magnetoresistive film into a single domain at laboratory level. At practical manufacturing levels, however, domain walls are formed to produce Barkhausen noise when the surface of a base substrate of a magnetoresistive head is rough, irregularities such as pinholes are present in the magnetoresistive film, pinholes are included in a film located adjacent to the magnetoresistive film and/or the magnetoresistive film is formed on a film having a stepped formation.
Further, conventional magnetoresistive heads are of the construction that an Fe-Mn alloy, an antiferromagnetic material, or a Co-Pt alloy, a permanent magnet material, of domain wall suppressing layers is exposed directly in an air bearing surface. The Fe-Mn alloy has poor corrosion resistance so that, when the Fe-Mn alloy is exposed in the air bearing surface, the characteristics of the domain wall suppressing layers are deteriorated to result in the occurrence of domain walls in the magnetoresistive film and, moreover, the magnetoresistive film and a shunt film and a soft film--both provided adjacent to the magnetoresistive film--are caused to corrode to a significant extent. As a consequence, the entire characteristics of the magnetoresistive head are deteriorated. On the other hand, the Co-Pt alloy is a ferromagnetic material and its exposure in the air bearing surface leads to the problem that a recording medium is demagnetized. To improve the corrosion resistance of a magnetic head, U.S. Pat. No. 4,825,325 discloses the formation of a capping layer over domain wall suppressing layers made of an Fe-Mn alloy and a magnetoresistive film. However, the troublesome exposure of an Fe-Mn alloy or Co-Pt alloy of domain wall suppressing layers in an air bearing surface has not been overcome.